Investigators aim to further the understanding of environmental factors that underlie the progression to Type 1 diabetes (T1D). Dysbiosis, defined as alterations in intestinal microbiota composition and function, has been hypothesized to increase the risk of developing T1D in those with genetic susceptibility. Dysbiosis may result from modern dietary habits, such as broad consumption of the highly processed Western Diet, or by widespread use of antibiotics. Here, investigators propose to examine the impact of dysbiosis on the endogenous innate inflammation known to exist within families affected by T1D and if probiotic supplementation may beneficially modulate this inflammatory state.

Participants will be asked to take the probiotic VSL#3 daily for six weeks. Stool and blood samples will be analyzed before and after the six week course of probiotics.

Inclusion Criteria:

1. Males and females 5-17 years of age
2. Full-sibling of an individual with a clinical diagnosis of Type 1 diabetes
3. Treatment naïve of any immunomodulatory agent
4. Naïve of any probiotic supplement within the past 12 months

Exclusion Criteria:

1. Presence of severe/active disease that interferes with dietary intake
2. Chronic use of medications known to affect gastrointestinal function, such as stool softeners or laxatives
3. Diagnosis of celiac disease and/or following a gluten-free diet
4. Presence of significant and sustained gastrointestinal symptoms within the prior 6 weeks (e.g., severe abdominal pain, worsening constipation, diarrhea, or recurrent nausea +/- vomiting)
5. Chronic inflammatory or autoimmune disease with the exception of well-controlled hypothyroidism or intermittent or mild persistent asthma not requiring the use of daily inhaled steroids
6. Use of any medications that could affect intestinal microbiota within the previous 3 months (e.g., antibiotics, prebiotics, or probiotics)
7. Any condition that, in the investigator's opinion, may compromise study participation or may confound the interpretation of the study results
8. Female participants of child-bearing age must not be pregnant